Kim Jong-un's aunt, the estranged wife of Jang Song-taek, who was purged and executed last month -- has either died of a heart attack or committed suicide, according to reports.

Kim Kyong-hui, previously a leading figure in the regime, is believed to have been ill for several years and was reportedly both treated for cancer and travelled to Russia last month for a heart complaint.

A source in the South Korean government was quoted in the 'Chosun Ilbo' as saying that the 67-year-old had either died from a heart attack or committed suicide.

The 'Daily NK', a dissident newspaper based in Japan, reported that Mrs Kim left North Korea for medical treatment after suffering a heart attack brought on by stress because of Jang's purge and execution.

She also apparently suffered from long-standing alcoholism and depression brought on by the suicide of her daughter in Paris in September 2006.

Mrs Kim was last seen in public on September 10, although her name was still on the list of dignitaries planning the funeral for a senior member of the Workers' Party in mid-December. Mrs Kim served as secretary for the party and held the rank of general in the Korean People's Army.

She was conspicuously absent from ceremonies to mark the second anniversary of the death of her brother, Kim Jong-il, on December 17, although an empty chair was placed on the podium at Kim Jong-un's right hand.

"It would not come as a surprise if she is indeed dead," said Toshimitsu Shigemura, a professor at Tokyo's Waseda University and an authority on North Korean affairs.

"She is not well, she has been treated for cancer and the alcoholism dates back about 30 years," he said.

PROP

It would not be a surprise if an announcement of Mrs Kim's death was delayed, he added, as she was such an important prop to Kim Jong-un's regime.

"If she is dead, then this is a serious problem for Kim Jong-un," he said. "As the sole daughter of the founder of the nation, she had both authority and legitimacy and she used that to protect Kim Jong-un's government. She was the sun and he was the moon.

"No one could go against her and she could force the party and the military to obey her orders by invoking her father's name," he said.

Prof Shigemura also suggested that the military was aware that Mrs Kim's health was failing and acted quickly against Jang in order to stop him inheriting her legitimacy.

"Her disappearance will inevitably cause a lot of political problems in Pyongyang," he added. "Kim Jong-un may be trying to cover her disappearance up for a while to consolidate his own political strength."

However, it was not possible to verify reports of her death.

Meanwhile, reports spread widely last week that Jang had been executed by throwing him to a pack of starving dogs.

It has since been shown that the story originated from a satirical post on the Chinese Tencent Weibo social networking site that was then picked up by media outlets around the world.

The story, which spread like wildfire after it was picked up by a Hong Kong-based newspaper, has created an image that Pyongyang's young ruler is even more brutal and unpredictable than previously believed.